1. Technical Field
The present invention relates generally to internal combustion engines in automotive vehicles and, more particularly, to a method of determining combustion stability of the engine and controlling the fuel injection pulsewidth to fuel injectors for the engine, especially following a cold start.
2. Discussion
Automotive vehicles commonly employ a port-injected internal combustion engine in which a fuel injector sprays fuel into air in an intake manifold of the engine near an intake valve of a cylinder as air gets pulled into the cylinder during the cylinder's intake stroke. The conventional fuel injector is typically controlled in response to a fuel injection pulsewidth signal in which the pulsewidth determines the amount of fuel injected into the corresponding cylinder of the engine. The fuel injection pulsewidth signal can be implemented to follow a programmed target fuel injection curve. The programmed target fuel injection curve determines the fuel injection pulsewidth and is generally utilized to provide adequate engine performance when feedback engine control is not available.
Many automotive vehicles commonly employ an oxygen (O.sub.2) sensor generally disposed upstream of the exhaust system for sensing the oxygen level in the exhaust gas emitted from the engine. The oxygen sensor can serve to provide a feedback signal to control engine operation and adjust fuel injection to the engine to achieve good engine performance. However, some conventional oxygen sensors are required to warm up to a sufficiently high temperature before an accurate oxygen sensor reading may be obtained. Also, following an engine start, the oxygen sensor and processing devices initially may not have acquired enough information to provide adequate feedback control. Therefore, for a period of time immediately following cold start up of the vehicle engine, the oxygen sensor may not be capable of providing accurate information with which the engine may be controlled to operate to achieve low hydrocarbon emissions. As a consequence, excessive hydrocarbon emissions may be emitted from the vehicle within the immediate period following start up of the engine.
Additionally, immediately following a cold engine start, the catalyst of the catalytic converter can be ineffective since the catalyst requires a period of time to warm up to a temperature at which the catalyst can operate effectively to burn excess hydrocarbons. As a consequence, hydrocarbon emissions may initially be high due to poor burning of the excess hydrocarbons due to a low temperature catalyst. To add to the problem, an over abundance of fuel in the catalyst may further cool the catalyst, thereby requiring an extended period of time for the catalyst to warm up to a sufficient operating temperature.
One approach for modifying fuel injection to the engine is described in U.S. Pat. No. 5,492,102, entitled "Method of Throttle Fuel Lean-Out for Internal Combustion Engines", issued to Thomas et al. on Feb. 20, 1996. The aforementioned issued U.S. patent in incorporated herein by reference. The approach described in the above-identified issued patent calculates a fuel lean-out multiplier value which is applied to a fuel pulsewidth value of the fuel injectors to reduce the amount of fuel injected into the engine by the fuel injectors. In the aforementioned approach, the fuel lean-out multiplier value is determined based off of a sensed throttle position and sensed deceleration.
It has also become increasing desirable to evaluate the combustion performance of the engine to improve control of the engine. In addition to controlling engine operation, combustion measurement can be used to evaluate hardware changes made to the engine. Combustion stability of the engine can be measured by processing engine speed signals taken over an angular displacement of the expansion stoke for each cylinder of the engine. By computing a roughness measurement of combustion, the combustion value can be used to control engine operation despite hardware changes.
It is therefore one object of the present invention to provide for control of a vehicle engine based on a learned measurement of combustion stability of the engine.
It is another object of the present invention to provide for a learned combustion stability value which may be employed to control engine operation while maintaining adequate driveability and performance of the vehicle.
More particularly, it is an object of the present invention to provide for a learned combustion stability value and apply the learned combustion stability value to modify the pulsewidth signal to fuel injectors of the engine so as to reduce the amount of fuel applied to the engine to reduce hydrocarbon emissions, especially following a cold engine start.